The present invention relates to molding compositions of wollastonite and phosphoric acid and to the fired products produced therefrom. The fired products are useful as electrically insulating materials, particularly electrically insulating materials for arc chutes of arc circuit breakers and other high temperature applications.
Report FH-11-7321 entitled "A Quick Setting SilicoPhosphate Cement" prepared for the Office of Research, Department of Transportation, Federal Highway Administration, Washington, D.C., and reproduced by the National Technical Information Service discloses a cold-setting cement for repair of concrete pavements utilizing calcine wollastonite and phosphoric acid wherein the acid contains metal ions such as zinc, aluminum and magnesium to develop hardness or strength.
C. E. Semler, "A Quick-Setting Wollastonite Phosphate Cement", Ceramics Bulletin, Volume 55, No. 11, pages 983-988 (1976) discloses a cold-setting cement utilizing wollastonite and phosphoric acid containing metal ions such as zinc, aluminum and magnesium.
Presently, insulating materials useful for high temperature applications contain asbestos. For example, the high temperature isulating material of U.S. Pat. No. 2,366,485 to Brink et al. incorporated herein by reference discloses a thermoset molded product produced by reacting under heat and pressure a reaction mixture of chrysotile asbestos fibers and ortho-phosphoric acid of a concentration exceeding 60%. However, medical evidence has indicated that asbestos is a health hazard. The present invention provides a substitute for asbestos-containing insulating materials.
The fired products of the present invention have a number of uses, but they are especially useful as electrically insulating materials, particularly for arc chutes of arc circuit breakers, such as that described in U.S. Pat. No. 3,440,378 to L. L. Baird, and U.S. Pat. No. 2,734,970 to N. A. Spears, Jr. which patents are incorporated herein for purposes of reference. The Spears patent specifically calls for asbestos compositions as insulating materials within arc chutes.